Magical Mystical NextGen and ADS-B

FAA air traffic controllers been seeing all sorts of videos at work about the FAA’s much touted NextGen air traffic system and ADS-B, apparently to get air traffic controllers excited about the new technology.

We’re beginning our training for ERAM, which is a computer system replacement that will have the capability to use all the whiz-bang features of NextGen, should they ever come to fruition. The schedule for ERAM however has already slipped due to development delays.

I finally starting looking into the details of ADS-B, a cornerstone of NextGen. ADS-B is designed to replace radar. Radar is the primary system air traffic controllers use to determine aircraft position (and keep the aircraft separated by the required distances).

One of the problems with radar is that it works along line of sight (like many radio waves). In hilly or mountainous terrain, the radar signal is blocked and thereby won’t detect aircraft, which means air traffic controllers can’t see where aircraft are on their radar displays.

It’s assumed that there is no radar coverage in the mountains, but few realize there are substantial areas of non-radar elsewhere in the United States, such as in central Iowa below 8,000 feet or so (the area where I work).

In these areas the controllers work the aircraft “non-radar” which relies on pilots to give verbal radio reports of their position based on their on-board navigation systems. It’s not real-time in that a controller must ask a pilot where he is at to determine his position should there be other air traffic in the area. Since the aircraft are constantly moving, the controller must get numerous reports from pilots to determine their positions to keep the aircraft separated.

Non-radar separation is much more tedious and involved than radar separation, for both controllers and pilots. Additionally the separation standards are increased in non-radar (we need to keep airplanes we can’t see on radar further apart just to be sure).

And unfortunately many of the fail-safes that exist in a radar environment disappear without radar. If pilots aren’t where they say they are (or where they’re supposed to be) there is no way for a controller to know. If a pilot gets too close to terrain or obstructions there is no way for a controller to realize that and warn him. There is no way for controllers to warn pilots of other air traffic or otherwise give traffic advisories.

The list goes on and on; needless to say it’s an air traffic separation technique used only in lieu of any other options and only in places where it’s expensive (or impossible) to install radar, or where the powers that be determined radar coverage wasn’t worth having (like lower altitudes in north central Iowa).

When I got hired by the FAA in 1988, I was told then in my initial indoctrination briefing that the FAA was working on satellite based radar. This was radar signals that would come from Earth orbiting satellites. Since there would be no terrain to obstruct downward-looking radar, non-radar would become a thing of the past. Of course this system never materialized, and the FAA continued its dependence on ground-based radar systems (with their associated non-radar areas).

So when the FAA started talking about the ADS-B “satellite-based” system it seemed that the problem of non-radar areas would finally be solved. The FAA started using ADS-B in Alaska’s mountainous terrain under the Capstone Project, which has now been absorbed under the ADS-B mantle. The elimination of non-radar areas in Alaska under the Capstone Project reduced the accident rate in certain areas by up to 40%.

The FAA encourages industry to install avionics equipment early and receive benefits from ADS-B sooner rather than later. ADS-B stands for Automatic Dependent Surveillance – Broadcast. It is the NextGen satellite-based technology that broadcasts traffic and flight information to pilots and air traffic controllers.

A “satellite-based” technology, most controllers assumed, meant that we wouldn’t have to be concerned about the line-of-sight limitations and we would eliminate non-radar completely!

Unfortunately what the FAA fails to mention (over and over) in their press releases is that ADS-B for air traffic control relies on receivers on the ground. Many of us mistakenly assumed that a “satellite-based” system meant that information would be relayed through satellites. (Aren’t we silly?!)

The way ADS-B works is that the aircraft avionics determines its position using global navigation satellites (GPS in the U.S.) and then transmits that information to a ground-based receiver, which sends it to the air traffic computers.

In other words, the aircraft knows its precise location, but the only way air traffic controllers get that information is if the aircraft transmits that information to a ground-based receiver. And guess what?

Those receivers on the ground are subject to almost the same line of sight limitations as radar!

Apparently the FAA isn’t looking for a dramatically better system for determining aircraft position for air traffic separation, as the coverage map indicates many of the same non-radar areas as currently exist using radar.

I naively believed that a 21st Century air traffic system would eliminate most of the non-radar areas in the continental U.S. Ah, dare to dream!

See that red spot in north central Iowa? That’s the airspace that I work that is non-radar now. With ADS-B the coverage increases a bit from 8,000 feet to 5,100 feet but the non-radar area isn’t eliminated.

So the problem of non-radar areas doesn’t go away at all, unless there are many receiver sites located in those areas, which currently the FAA has no intention of installing. Sure, the ADS-B receiver sites are cheaper to install than radar, but will they be eventually installed in those non-radar areas?

In essence, the FAA wants to turn off many of its radar sites (and save the money on maintaining them), and replace them with avionics that the aircraft owner will have to pay for, install and maintain, and with cheaper ADS-B receiver sites on the ground (contracted out of course) and the GPS system that already exists.